1. Field of the Invention
The invention relates to a crosslinkable molding material which contains a silane-grafted poly-.alpha.-olefin.
2. Discussion of the Background
Polymers and polymer blends have for years become increasingly popular as materials which can be processed by a thermoplastic method. However, there is a substantial dependence of important performance characteristics, such as, for example, impact strength, tensile strength and tendency to creep, on the molecular weight. For this reason, the polymeric material should have as high a molecular weight as possible in order to possess a high impact strength, a high tensile strength and only a small tendency to creep in the finished article. However, when the molecular weight increases, the melt becomes so highly viscous that it can scarcely be processed. For this reason, if readily processible molding material is desired, it is necessary to make a compromise and accept a poorer impact strength and higher tendency to creep. This applies in particular to injection molding materials, which must be particularly readily flowable.
A further problem is encountered in the case of polymer blends. Since most polymers are incompatible with one another, it is initially possible, with strong shearing, to distribute one blend component in dispersed form or as a network in the other blend component. However, if the melt then enters a zone of low shearing or no shearing, for example a mold, the initially finely divided phase coalesces to larger droplets. The article obtained is thus extremely brittle after solidification and hence unusable.
In special cases, it is possible to achieve good dispersibility without subsequent coalescence by chemically linking the two blend components. In such cases, the two phases adhere to one another. The extent of the adhesion is frequently not sufficient, however, to achieve the desired high impact strength. This problem occurs if one attempts to impart impact strength to thermoplastic polyesters, such as polyethylene terephthalate or polybutylene terephthalate, by incorporating, or compounding rubbers which are functionalized, for example maleic anhydride-functionalized ethylene/propylene rubber (EPM) or ethylene/propylene/diene rubber (EPDM). For a sufficient reaction of the terminal OH groups of the polyester with the anhydride groups of the rubber, a subsequent solid-phase postcondensation is required, which gives rise to high process costs.
Therefore, there is a continuing need to provide molding materials which are readily processible and nevertheless give shaped articles having very high impact strength, high tensile strength and very small tendency to creep.
There is also a need for molding materials into which blend components can be readily mixed to form blends having stable phases.
There is also a need for polymer blends that have stabilized morphology and in which there is strong phase adhesion at the boundary.